Raiders smashed their way into an empty priest’s house before trashing and flooding it.
After getting into Christ the King’s former presbytery, in Gateside Drive, Grange Park, the vandals shattered windows and smashed up furniture, including ceramic toilets and sinks.
They then turned on taps upstairs, leaving the disused building to flood as they made their escape, at some point between late afternoon on Friday and Saturday morning, police said.
The attack has been slammed by a local leader.
Terry Bennett, chairman of the Grange Park Community Partnership, said: “It’s just mindless vandalism. I can’t understand the motivation to do it.
“What do they stand to gain from it?
“It’s fairly quiet down there nowadays. It’s a lot quieter than it used to be, so this comes as a total surprise to me.”
The church was founded in 1949 but closed several years ago, with masses held in Christ the King School until a new church opened in 2014, next to the multi-million pound redevelopment of St Mary’s Catholic College and Christ the King Catholic Primary School.
In February, it was revealed the presbytery and car park were set to be bought by the council for around £140,000.
The site, measuring around half an acre, is beside the Cherwell Centre and Chepstow Road shops, and forms part of the town hall’s future housing plans.
A spokesman yesterday said negotiations to buy the building were ongoing, but no deal with the church as yet been reached.
Security at the adjacent boarded up youth club and church, which are already owned by the council, is believed to be sufficient enough to deter vandals, he added.
A spokesman for Lancashire Police said the break-in and damage happened between 4.30pm on Friday, and 10.15am on Saturday.
She said: “Offenders have approached the side of a disused church, made their way inside through a window, and have some smashed some furniture that was in the building.
“They have smashed some windows upstairs and downstairs, as well as some ceramic toilets and basins.
“They have damaged the back door, and turned on some taps upstairs before leaving.
“The break-in is under investigation. No arrests have been made.”
Any information can be reported to police by calling 101, quoting log reference number WA-16-07-301.